In recent years, lithium ion batteries and other sealed batteries (typically secondary batteries) have become more and more important as vehicle-mounted power sources and as power sources for computers, portable devices and the like. Lithium ion batteries in particular provide high energy densities with low weight, which makes them attractive as vehicle-mounted high output power sources.
Meanwhile, lithium ion batteries produce heat if they are overcharged due to operational error, improper use or the like, and may even overheat. To prevent overheating during overcharge, it has been proposed for example that the internal pressure of the battery could be elevated by means of CO2 gas generated by an electrochemical decomposition reaction of lithium carbonate contained in the materials making up the positive electrode, and a current interruption mechanism could be operated by means of this rise in internal pressure. Patent Documents 1 to 3 are given as documents of prior art relating to this type of technology.    Patent Document 1: Japanese Patent Application Laid-open No. H05-242913    Patent Document 2: Japanese Patent Application Laid-open No. H05-151997    Patent Document 3: Japanese Patent Application Laid-open No. H05-182667